Conventionally, a power converter that adjusts an AC power outputted from a generator and converts it to a DC power is used for, for example, charging a battery of a vehicle.
FIG. 34 is a configuration of a conventional power converter 200. In FIG. 34, an AC power is fed to a generator coil 100 by driving a rotation axis of the generator. A thyristor 201, a resistor 202, a diode 203, Zener diodes 204 and 205, and a diode 206 constitute the power converter 200, being basically realized as a half-wave rectifier circuit.
Specifically, an anode of the thyristor 201 is connected to one end of the generator coil 100, and a cathode thereof is connected to a positive electrode of a battery 300 that forms a load of the power converter 200. The resistor 202, the diode 203, and the Zener diodes 204 and 205 are connected in series in that order between the anode and the ground of the thyristor 201. From the anode of the thyristor 201 toward the ground, the diode 203 is connected in the forward direction, and the Zener diodes 204 and 205 are connected in the reverse direction. The diode 206 is connected in the forward direction from a connection point P between the resistor 202 and the diode 203 toward a gate electrode of the thyristor 201.
A voltage Vref at the connection point P is set such that the thyristor 201 is controlled to an ON state when a terminal voltage of the battery 300 is below a target voltage VT, which is higher than a stipulated voltage of the battery 300 by a predetermined voltage. In other words, the voltage Vref is set at an appropriate value such that the thyristor 201 does not attain the ON state when the terminal voltage of the battery 300 is equal to or greater than the target voltage VT.
A power converter according to the abovementioned conventional technique will be explained using FIG. 35.
FIG. 35A is a diagram of an operation where a generator has a low number of rotations, and FIG. 35B, an operation where the generator has a high number of rotations. For sake of convenience, an initial value of the terminal voltage of the battery 300 is lower than the target voltage VT.
In a period T1 in FIG. 35A, when a positive phase (positive voltage) of an AC voltage VA fed to the generator coil 100 is supplied to the anode of the thyristor 201, the AC voltage VA is applied via the resistor 202 to the connection point P. When the voltage at the connection point P increases, current flows to the gate electrode of the thyristor 201 via the diode 206, and the thyristor 201 turns ON. Thereafter, the Zener diodes 204 and 205 clamp the voltage at the connection point P to the voltage Vref. When the thyristor 201 turns ON, the positive phase of the AC voltage VA is supplied via the thyristor 201, whereby the output voltage VO of the thyristor 201 increases, charging the battery 300.
In a subsequent period T2, when the AC voltage VA shifts to the negative phase (negative electrode), the voltage at the connection point P decreases, whereby the thyristor 201 switches to a reverse-bias state and turns OFF. When the thyristor 201 turns OFF, since power is no longer supplied to the battery 300, the battery 300 discharges and its terminal voltage gradually decreases.
In a subsequent period T3, when the AC voltage VA shifts again to the positive phase, the voltage at the connection point P increases; however, since the terminal voltage of the battery 300 (i.e. the output voltage VO of the thyristor 201) is still higher than the target voltage VT, current does not flow to the gate electrode of the thyristor 201, which remains OFF. The thyristor 201 remains OFF in subsequent periods T4 to T6, since the output voltage VO is still higher than the target voltage VT.
During a subsequent period T7, when the output voltage VO drops below the target voltage VT, the thyristor 201 turns ON and the output voltage VO is slightly increased by the positive phase of the AC voltage VA being outputted from the generator at that time, charging the battery 300.
While, in a subsequent period T8, when the AC voltage VA shifts to negative phase, the thyristor 201 turns OFF and the output voltage VO decreases, in a subsequent period T9, when the output voltage VO drops below the target voltage VT, the thyristor 201 turns ON, and output voltage VO is increased by the positive phase of the AC voltage VA being outputted from the generator at that time.
Thus, when the output voltage VO drops below the target voltage VT, the thyristor 201 turns ON and charges the battery 300 during the positive phase of the AC voltage VA.
As shown in FIG. 35B, when the generator has a high number of rotations, the amplitude of the AC voltage VA outputted from the generator increases and so does its frequency, thereby increasing the rise rate of the output voltage VO, but it is otherwise identical to the example of FIG. 35A.
Patent Literature: JPA No. Hei 10-52045.